1. Field of the Invention
The present invention relates to a trip device of a circuit breaker to break such a high current as short-circuit current as quickly as possible.
2. Description of the Background Art
There is a circuit breaker which is enclosed in a casing formed of an insulating molding. The circuit breaker is composed of switching contacts, an operating mechanism which opens/closes the switching contacts, a trip device which automatically releases a trip latch mechanism, when overcurrent flows, for working the operating mechanism to open the switching contacts, and an arc-extinguishing device for irresistibly extinguishing arc which is generated when the switching contacts are opened so as to break the current.
Generally, in an electric circuit, if the circuit breaker breaks an enormous abnormal current which occurs due to a short-circuit accident in the electric circuit as immediately as possible to limit the current flowing through the circuit to a small magnitude, the damage to the electric circuit can be made minimum and accordingly the damage to the circuit breaker itself can be reduced. Therefore, the circuit breaker which can more speedily break the short-circuit current can accordingly break a high short-circuit current immediately, so that the rated breaking capacity thereof can be increased.
The electromagnet is applied to a trip device of a conventional circuit breaker which operates upon occurrence of a short-circuit current. The electromagnet operates when the current flowing through a main circuit conductor of the circuit breaker exceeds a predetermined threshold so as to release the trip latch mechanism included in the operating mechanism and thus open the switching contacts.
Such an electromagnet is slow in operation due to inertia of a movable core, and thus it is impossible to break more speedily the short-circuit current when the current exceeds a threshold. In particular, when an enormous abnormal current flows to cause the switching contacts to repel each other due to the electromagnetic force and consequently the switching contacts are opened, the contacts could be brought into contact again unless the trip latch mechanism is immediately released. In such a case, the circuit breaker itself could suffer a great damage.